The overall goal of this Program Project Grant is to develop new animal models in which to investigate metabolic pathways that regulate plasma lipoproteins and cholesterol homoeostasis. The major focus of this proposal will be to use transgenic animals (mice and rabbits) that overexpress or fail to express specific genes involved in lipoprotein and cholesterol metabolism in order to understand the physiological function of these proteins and the consequences of their malfunction. Development of these animal models should provide new insights into the function of apolipoprotein (apo-) C-I, apo-C-II, apo-E, hepatic lipase, apo-B, apo-B mRNA editing factor(s), and the acetyl low density lipoprotein (LDL) receptor. Moreover, studies using animals in which the function of a single component is altered should enhance our understanding of the complex interactions among lipids, apolipoproteins, and plasma enzymes that constitute lipoprotein pathways and regulate plasma cholesterol levels. The studies are designed to elucidate the role of apo-C-I, apo-C-III, and variant forms of apo-E in chylomicron remnant catabolism; the role of the acetyl LDL receptor in atherosclerosis; and the role of the hepatic form of apo-B (apo-B100) and the intestinal form of apo-B (apo-B48) in lipoprotein metabolism. In addition, cell biology studies will focus on the synthesis of apo-B-containing lipoproteins, the mechanisms of apo-B mRNA editing, and the regulation of expression of the acetyl LDL receptor. A multidisciplinary approach will be used for these studies, including many modern techniques from cell biology, immunology, electron microscopy, pathology, genetics, biochemistry, and animal physiology. In addition, this proposal has three major technical objectives: (1) to establish gene targeting by homologous recombination, which will permit the defined modification of wild-type genes; (2) to develop transgenic rabbits, which will provide a larger animal model whose lipoprotein physiology and atherosclerosis are similar to those of humans; and (3) to develop negative dominant mutations in transgenic rabbits, which will permit the elimination of specific gene function without resorting to homologous recombination. The generation of transgenic animals in which key genes in lipoprotein metabolism can be selectively deleted or expressed will contribute to an increased understanding of the molecular basis of cholesterol metabolism, the causes of hyperlipidemia in humans, and the pathogenesis of atherosclerosis. In addition, animal models with gene defects that cause specific lipoprotein disorders will be useful for testing therapeutic interventions.